Spark discharge lamp having a predetermined ratio between the cross-section of the electrodes and the inner surface of the tube



Aug. 31, 1965 F. FRUNGEL SPARK DISCHARGE LAMP HAVING A PREDETERMINED RATIO BETWEEN THE CROSS-SECTION OF THE ELECTRODES AND THE INNER SURFACE OF THE TUBE Filed July 10, 1961 SUP/ 1. Y

United States Patent 8 Claims. ((51. 315-241 The present invention concerns spark discharge lamps, and particularly a type of lamp which is extremely useful for emitting light signals for the purpose of measuring visibility under varying atmospheric conditions and for determining the existence of fog in the atmosphere.

It is well-known that an accurate quantitive measurement of the absorption of light by its passage through a more or less permeable medium are severely hampered by variations of the intensity of the light emitted by the respective source of light. Such variations of the intensity of the emitted light are often due to a change in the structure of the light source. For instance, in the case of incandescent lamps the material of the filament gradually evaporates, and in the case of spark discharge lamps the ends of the spark electrodes gradually disintegrate. In both cases the material lost by the filament or by the electrodes, respectively, is dissipated and deposited as a black layer on the inner surface of the respective bulb. This layer increasingly affects the light permeability of the bulb wall and thus introduces an additional factor of absorption of not precisely determined magnitude into the process of measuring the light absorption in the atmosphere.

For overcoming this difficulty various means and methods have been proposed for compensating variations in the emission of light from the source of light. However, it has been found that all these methods and means are rather involved and expensive, and that these known methods and means are particularly unsuited for being applied to spark discharge lamps without substantial difficulties.

It is therefore a main object of this invention to provide for a system capable of keeping the amount of light emitted by spark discharge lamps substantially constant for a considerable time of operation.

It is another object of this invention to provide for a system of the type set forth which does not require any outside regulating and compensating devices.

It is still another object of this invention to provide for a system as set forth according to which the required parameters of the spark discharge lamp can be easily determined by simple experimentation.

With above objects in view, a spark discharge lamp having a gas-filled transparent bulb and a pair of spark electrodes spaced from each other to form a spark gap which increases gradually by disintegration of the electrode material under the action of repeated spark discharges, the disintegrated electrode material being dispersed and deposited as a substantially uniform layer on the inner surface of the transparent bulb, is characterized, according to the invention, in that the ratio between the cross-section of the electrodes and the inner surface of the bulb is such that the reduction of light permeability of the bulb by the deposited layer of electrode material is compensated by the increase of light output of the spark discharge which increase is caused by the increase of the spark gap by the disintegration of electrode material, whereby the amount of the light emitted from the lamp by consecutive spark discharges therein is maintained substantially constant in spite of increasing thickness of the layer of electrode material deposited on the inner surface of the bulb.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing in which a spark discharge lamp arrangement incorporating the invention is diagrammatically illustrated.

The circuit shown in the drawing is of a conventional type and comprises a source of high voltage energy 1 which is connected incircuit with an impulse capacitor 2 for charging the latter. A spark discharge lamp 4 is connected in parallel with the capacitor 2 by short leads 3 having low inductivity. The spark discharge lamp 4 comprises a transparent bulb shown in section and made of hard glass or quartz, a filling of gas 7, and at least two spark electrodes 5. In certain special cases it is advisable to provide also a separate igniting electrode 6.

It is advisable to use as a source for high voltage energy supply a device the power output of which is constant on account of a hyperbolic voltage-current characteristic. The gas filling 7 should be one of the heavier rare gases because hereby the duration of the desired performance of the lamp according to the invention is prolonged. The rare gas should be chosen so that it would not attack the electrode material.

An impulse discharge lamp as described and shown may be operated in the illustrated circuit for instance at a rate of 5 to 10 spark discharges per second. As can be seen the circuit contains no separate or additional compensating or regulating devices. As high voltage energy is applied to the capacitor 2 the latter is charged, and as soon as the potential at the capacitor reaches the breakdown potential of the spark gap between the electrodes 5, the capacitor 2 discharges across the spark gap and pro duces the desired spark.

In the course of continued operation of a spark discharge lamp of the type described it is inevitable that the electrode material at the tips thereof is gradually disintegrated under the action of the repeating spark discharges. Consequently electrode material is dispersed and deposited as a black layer along the inner surface 8 of the bulb. As the thickness of this layer of electrode material increases the optical permeability of the bulb decreases, and accordingly decreases the emission of light from the lamp per spark discharge.

However, it has to be taken into consideration that due to the disintegration of electrode material the spark gap increases so that concurrently with the increase of the spark gap also the breakdown potential necessary for the development of a spark also increases. The energy stored in a capacitor of a capacity C and charged to a potential E is U=.5 CE Since upon a spark discharge the entire stored capacitor energy is converted into light energy, the output of light increases in proportion with the square of the breakdown voltage. If, at an initial stage of the operation, the spark gap is determined by a spacing d between the tips of the electrodes 5, the corresponding breakdown voltage is E and the resulting output of light is L, then the increase of the spark gap to a dimension al will result in an increased breakdown volt age E and in a corresponding increased light output L This may be expressed by the following equation:

L E d tiara? As stated above the increase of the spark gap dimension is necessarily associated with a deposit of electrode L=ktL It is well-known in the art to predetermine the breakdown or spark voltage of a spark discharge lamp depending upon the size of the spark gap and the nature and the pressure of the gas filling. With this in mind it is possible according to the invention to obtain the desired performance according to the Equation 2 by properly selecting the dimensions of certain components of the lamp, or rather the ratio between the dimensions of such components.

other hand, a deposit layer of a thickness t=.5,u applied to the surface A of 4,800 mm. represents 2.4 mm. of electrode material. This amount, in turn, corresponds, for electrodes of 1.2 mm. to Ad of 2 mm. i.e. a shortening of each electrode by 1 mm.

The 50% absorption of light is to be compensated by a corresponding 50% increase of light emission from the spark. This can be achieved if during the 2 mm. increase of the spark gap the spark voltage is increased according to Equation 1, eg from 3 kv. to 3.7 kv. because in this case the squares of these voltage values have a ratio of 9113.5 which represents an increase of light energy in the amount of 50%. This condition is met if the initial spark gap is 8.4 mm. because, with a gas filling of Xenon at normal atmospheric pressure, an initial breakdown or spark voltage of 3 kv. rises to 3.7 kv. when the spark gap has grown to 10.4 mm.

.The chart herebelow will serve to illustrate the performance of the spark discharge lamp having the above mentioned characteristics and dimensions.

The variables to be selected in this manner are the cross-section of the electrodes 5 and the area of the inner surface of the bulb. The electrode material disintegrated during an increase of the spark gap from d to d must be equal to the material deposited as a layer of the thickness 2 on the inner surface A of the bulb. This is expressed by the equation:

In above equation q represents the cross-section of the electrodes 5. Preferably these electrodes are, at least in the neighborhood of their tips, preferably cylindrical or prismatic. However, even if they are conical or pyramidal the result is not substantially different.

From the Equation 3 the following equations can be derived:

At QEZ It can be seen from the Equations 4 and 5 that as soon as the relation between t and Ad is known or established, the size of the bulb i.e. the size of its inner surface area can be chosen depending upon the electrode cross-section q, :or the cross-section q can be chosen depending upon a given inner surface area A of the bulb.

Before describing in what manner the relation between t and Ad is determined, an example of a suitable combination of components will be described.

In this example, the capacitor 2 is constituted by a condenser battery of 30,000 pf. which is connected 'by conductors 3 having an inductivity of only about .1 ,uH with a discharge lamp filled with Xenon at 1 atm. and having an inner surface area of 48 cm. or 4,800 mm. The material of the electrodes 5 is tungsten and their cross-section is 1.2 mm. By separate experiments it has been established that the light filter factor k of tungsten amounts to about 100% per Lu. This means that the above mentioned factor kt in the case of a deposit layer having a thickness of .5 1 would result in a 50% absorption of the light emitted from the spark. On the It can be seen from the above chart that the light output increases gradually to 50% and that also the absorption caused by the deposit of electrode material in the same amount as the disintegrated electrode material results also in an increasing absorption of light matching very closely the increase of light output.

Extensive experiments with a spark lamp of the above described characteristics has shown that the compensation according to Equation 2 has been accomplished very satisfactorily through an operation of the particular lamp through two years with a spark rate of 10 sparks per second, the accuracy of the compensation or, in other words, the mean value of the peak light peak values of the sparks, remaining constant within about 2%.

It may be mentioned here that the arrangement above described may be advantageously supplemented by scattering mirrors which, as is well-known, compensate the shimmying behaviour of the spark which do not remain always in line with the common axis of the electrodes so that an integration of a plurality of sparks, otherwise necessary in certain measuring procedures for obtaining a uniform measured value, is rendered unnecessary.

As mentioned above, it is necessary to determine the relation between the deposit layer thickness t and the corresponding increase of the spark gap Ad. This can be achieved easily by a simple experiment. The experiment is carried out with a spark discharge lamp having all the characteristics of the lamp described above but may have a different size and therefore a different inner surface area. Assuming that the experimental lamp having all the characteristics mentioned above has an inner surface area A of 2400 mm. After a certain time of spark production it would be found that the deposit layer has grown to a thickness t of .75 while the spark gap has increased by an amount Ad of 1.5 mm. As can be seen from the above chart this increase of the spark gap would correspond to an increase of light output amounting to 38%. The amount of disintegrated electrode material is again 1.8 mm. On the other hand, the amount of electrode material deposited on the inner surface area of the bulb would be in this case .75 2400=1.8 mmfi. This is in accordance with Equation 3. However, the absorption factor kt would be in this case 75%. Therefore, the experimenter would recognize that the absorption has increased 75% while the output of light has increased only 38%. From this he can draw the conclusion that the design of the lamp has to be changed either by reducing the cross-section q from 1.2 to .6 mm. or by increasing the inner surface area A to 4800 mm. because in either case the thickness of the deposit layer would be correspondingly reduced and the absorption would become equal to the increase of light output as shown in the above chart.

It should be understood that particularly long duration of the above-described compensation effect according to the invention can be achieved if the lamp is filled with one of the heavier rare gases. For instance, if Argon if used, the compensation effect is only maintainable through a number of months. However, if Xenon is used, the very fine dust of electrode material is slowed down irrespective of the energy of the discharge whereby the speed of increase of the blackening deposit layer is reduced. Consequently the compensation effect according to the invention will continue satisfactorily through years.

In addition, the filling gas should be so selected that the ions formed with every spark discharge do not react chemically with the electrode material. For instance, Argon ions are as active as atomic chlorine and attack strongly the electrode material as for instance tungsten, While Xenon ions correspond approximately to Iodine and therefore attack the electrode material to a much lesser degree. This results in a reduction of the disintegration of the electrode material.

It has been mentioned above that the high voltage supply apparatus should have a hyperbolic characteristic so that always the product of current and voltage is constant. The advantage of such an arrangement is that the discharge vessel or bulb remains always uniformly sub jected to heat input irrespective of an increase in the spark voltage.

While a spark discharge lamp according to the invention is of particular advantage and usefulness in the determination of visibility under various atmospheric conditions, this type of lamp is quite as well useful in all other fields of photometry.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of a spark discharge lamp differing from the types described above.

While the invention has been illustrated and described as embodied in a spark discharge lamp having a gas-filled transparent bulb, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the presentinvention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A spark discharge lamp having a gas-filled transparent bulb and a pair of spark electrodes spaced from each other to form a spark gap which increases gradually by disintegration of the electrode material under the action of repeated spark discharges, the disintegrated electrode material being dispersed and deposited as a substantially uniform layer on the inner surface of the transparent bulb, characterized in that the ratio between the crosssection of the electrodes and the inner surface of the bulb is such that the reduction of light permeability of the bulb by the deposited layer of electrode material is compensated by the increase of light output of the spark discharge 6 which increase is caused by the increase of the spark gap by the disintegration of electrode material, whereby the amount of light emitted from the lamp by consecutive spark discharges therein is maintained substantially constant in spite of increasing thickness of the layer of electrode material deposited on the inner surface of the bulb.

2. A spar-k discharge lamp having a gas-filled transparent bulb and a pair of spark electrodes spaced from each other to form a spark gap which increases gradually by disintegration of the electrode material under the action of repeated spark discharges, the disintegrated elec trode material being dispersed and deposited .as a substantially uniform layer on the inner surface of the transparent bulb, characterized in that the ratio between the cross-section q of the electrodes and the inner surface A of the bulb is such that A/q=Ad/t wherein Ad is the increase of the spark gap due to disintegration of electrode material, and wherein t is the thickness of the deposited layer thereof on the surf-ace A, and that the reduction of light permeability of the bulb, in proportion to the light filter factor k multiplied with the thickness of the deposited layer I, wherein k is a coefficient of the electrode material, is compensated by the increase of light output of the spark discharge from a value L to a value L which increase is caused by the increase Ad of the spark gap, whereby the amount of light emitted from the lamp by consecutive spark discharges therein is maintained substantially constant according to L=ktL in spite of increasing thickness of the layer of electrode material deposited on the inner surface of the bulb.

3. A spark discharge lamp according to claim 2, wherein the bulb is filled with a rare gas of an atomic weight of at least 83.80 whereby the rate of disintegration of the electrode material is reduced.

4. A spark discharge lamp according to claim 2, wherein the bulb is filled with Xenon whereby the rate of disintegration of the electrode material is reduced.

5. A spark discharge lamp according to claim 2, Wherein the bulb is filled with a rare gas which, even when ionized by spark discharges, is incapable of reacting chemically with the electrode material.

6. A spark discharge lamp according to claim 2, wherein the electrode material is tungsten and wherein the bulb is filled with Xenon.

7. A spark light system, comprising, in combination, a transparent wall discharge vessel filled with .a gaseous medium and having a predetermined inner surface area; spark gap means arranged within said vessel and including electrodes of predetermined cross-section and spaced from each other to form a spark gap of a predetermined starting dimension which gradually increases du to disintegration of said electrodes under the action :of repeated spark discharges, said electrodes being made of a material chemically unaffected by said gaseous medium; and discharge circuit means including a discharge condenser connected with said spark gap means, the inductance of said discharge circuit means in combination with said spark gap means establishing a predetermined discharge characteristic causing emission of non-oscillating light flashes when said condenser is dis-charged across said spark gap means, said discharge characteristic being so chosen that the ratio between the discharge energy of said discharge condenser and said inner surface area of said vessel predetermines the rate of formation, on said inner surface area, of a layer of electrode material resulting from said electrode disintegration and thus causing a gradually decreasing light permeability of said vessel, the ratio between said cross-section of said electrodes and said inner surface area of said vessel being such that the reduction of light permeability of said vessel by the deposited layer of electrode material is compensated by the increase in light output of the spark discharge caused by said increase of said spark gap dimension.

8. A spark light system, comprising, in combination, a transparent wall discharge vessel filled with a gaseous medium and having a predetermined inner surface area; spark gap means arranged Within said vessel and including electrodes of predetermined cross-section and spaced from each other to form a spark gap of a predetermined starting dimension which gradually increases due to disintegration of said electrodes under the action of repeated spark discharges, said electrodes being made of a material chemically unaffected by said gaseou medium; discharge circuit means including a discharge condenser connected with said spark gap means, the inductance of said discharge circuit means in combination with said spark gap .means establishing a predetermined discharge characteristic causing emission of non-oscillating light flashes when said condenser is discharged across said spark gap means, said discharge characteristic being so chosen that the ratio between the discharge energy of said discharge condenser and said inner surface area of said vessel predetermines the rate of formation, on said inner surface area, of a layer of electrode material resulting from said electrode disintegration and thus causing a gradually decreasing light permeability of said vessel, the ratio between said cross-section of said electrodes and said inner surface area of said vessel being such that the reduction of light permeability of said vessel by the deposited layer of electrode material is compensated by the increase in light output of the spark discharge caused by said increase of said spark gap dimension; and source means of high voltage electric energy for charging said discharge condenser and having a hyperbolic characteristic determining a constant wattage output irrespective of voltage or current variations.

References Cited by the Examiner UNITED STATES PATENTS 2,682,007 6/54 Hi-lder eta'l 313220 X 2,774,013 12/56 Wil-louglrby 3l32'14 X DAVID J. GALVIN, Primary Examiner.

JOHN W. HUCKERT, Examiner. 

8. A SPARK LIGHT SYSTEM, COMPRISING, IN COMBINATION, A TRANSPARENT WALL DISCHARGE VESSEL FILLED WITH A GASEOUS MEDIUM AND HAVING A PREDETERMINED INNER SURFACE AREA; SPARK GAP MEANS ARRANGED WITHIN SAID VESSEL AND INCLUDING ELECTRODES OF PREDETERMINED CROSS-SECTION AND SPACED FROM EACH OTHER TO FORM A SPARK GAP OF A PREDETERMINED STARTING DIMENSION WHICH GRADUALLY INCREASES DUE TO DISINTEGRATION OF SAID ELECTRODES UNDER THE ACTION OF REPEATED SPARK DISCHARGES, SAID ELECTRODES BEING MADE OF A MATERIAL CHEMICALLY UNAFFECTED BY SAID GASEOUS MEDIUM; DISCHARGE CIRCUIT MEANS INCLUDING A DISCHARGE CONDENSER CONNECTED WITH SAID SPARK GAP MEANS, THE INDUCTANCE OF SAID DISCHARGE CIRCUIT MEANS IN COMBINATION WITH SAID SPARK GAP MEANS ESTABLISHING A PREDETERMINED DISCHARGE CHARACTERISTIC CAUSING EMISSION OF NON-OSCILLATING LIGHT FLASHES WHEN SAID CONDENSER IS DISCHARGE ACROSS SAID SPARK GAP MEANS, SAID DISCHARGE CHARACTERISTIC BEING SO CHOSEN THAT THE RATIO BETWEEN THE DISCHARGE ENERGY OF SAID DISCHARGE CONDENSER AND SAID INNER SURFACE AREA OF SAID VESSEL PREDETERMINES THE RATE OF FORMATION, ON SAID INNER SURFACE AREA, OF A LAYER OF ELECTRODE MATERIAL RESULTING FROM SAID ELECTRODE DISINTEGRATION AND THUS CAUSING A GRADUALLY DECREASING LIGHT PERMEABILITY OF SAID VESSEL, THE RATIO BETWEEN SAID CROSS-SECTION OF SAID ELECTRODES AND SAID INNER SURFACE AREA OF SAID VESSEL BEING SUCH THAT THE REDUCTION OF LIGHT PERMEABILITY OF SAID VESSEL BY THE DEPOSITED LAYER OF ELECTRODE MATERIAL IS COMPENSATED BY THE INCREASE IN LIGHT OUTPUT OF THE SPARK DISCHARGE CAUSED BY SAID INCREASE OF SAID SPARK GAP DIMENSION; AND SOURCE MEANS OF HIGH VOLTAGE ELECTRIC ENERGY FOR CHARGING SAID DISCHARGE CONDENSER AND HAVING A HYPERBOLIC CHARACTERISTIC DETERMINING A CONSTANT WATTAGE OUTPUT IRRESPECTIVE OF VOLTAGE OR CURRENT VARIATIONS. 